Dental floss having low density and method of making same

ABSTRACT

A dental floss comprising a porous PTFE fiber having a density of less than about 0.7 g/cc. The inventive floss is abrasion resistant, grippable and has a soft feel to the hands and a rough feel in the mouth. The floss is made by an extrusion process with non-contact heating during subsequent expansion with amorphous locking.

RELATED APPLICATIONS

[0001] This application is a continuation of application Ser. No.10/339,787, filed Jan. 9, 2003, which is a divisional of applicationSer. No. 09/449,078, filed Nov. 24, 1999, which issued as U.S. Pat. No.6,539,951 on Jan. 6, 2003, which is a continuation-in-part ofapplication Ser. No. 09/387,691, filed Aug. 31,1999.

FIELD OF THE INVENTION

[0002] The present invention relates to dental floss and, moreparticularly, to a dental floss having a low density.

BACKGROUND OF THE INVENTION

[0003] Use of dental floss remains one of the most recommended ways ofpreventing and controlling gum disease. Several types of floss arecurrently known and used. These flosses are made of materials such asnylon, polyethylene, ultra-high molecular weight polyethylene,polytetrafluoroethylene (PTFE), and expanded PTFE (ePTFE). Of these,ePTFE floss, and particularly monofilament ePTFE floss, is particularlypreferred, in part because of its inherently low friction propertieswhich allow it to slide between teeth more easily.

[0004] Certain characteristics are typically considered desirable fordental floss. First, the floss should be abrasion resistant such that itdoes not shred, fray, or otherwise break during use when passed betweena user's teeth. In order to be used effectively, the dental floss shouldalso be grippable; that is, able to be grasped by a user's hands orother device for manipulation between the teeth without slipping in thehands or other device. Several attempts have been made at making PTFEflosses more easily grippable. As discussed in U.S. Pat. No. 5,518,012to Dolan, et al., for example, a waxed coating may be placed over thePTFE fiber in order to make the floss more grippable. In U.S. Pat. No.5,911,228 to Curtis, et al, a solid additive is incorporated within thePTFE fiber structure in order to make the fiber grippable without theneed for any coating. A grippable PTFE floss that did not require theuse of either a coating on the fiber or additives within the fiber inorder to make it grippable, would be desirable.

[0005] A dental floss should also have the subjective advantage ofhaving a good “feel” for the user. The feel includes the overallhandling characteristics of the fiber as well as the perceived effect ofthe fiber in a user's mouth as it cleans the teeth. Desirably, a PTFEdental floss should be soft and conformable to slide comfortably betweena user's teeth, while at the same time providing a scrubbing or cleaningsensation for the user when manipulated under the gums. The floss shouldhave a soft feel to the hands and a rough feel in the mouth.

[0006] A PTFE floss having all of these advantages and characteristicswould be desirable.

SUMMARY OF THE INVENTION

[0007] The present invention provides a dental floss comprising a fiberhaving a denier between 100 and 3,500 and having a density of less thanabout 0.8 g/cc, with additional ranges for alternative embodiments ofless than about 0.7 g/cc, less than about 0.6 g/cc, less than about 0.5g/cc, less than about 0.4 g/cc, less than about 0.3 g/cc, and less thanabout 0.2 g/cc. The floss has a strength suitable for use as a dentalfloss, typically greater than about 1.5 lbs, with additional ranges foralternative embodiments of greater than about 2 lbs, greater than about2.5 lbs, greater than about 3 lbs, greater than about 5 lbs, greaterthan about 7.5 lbs, and greater than about 10 lbs. The floss may be ahollow fiber with any desired cross-section, such as substantiallyelliptical or rectangular. The floss is also abrasion resistant, havingan average abrasion break strength in various embodiments of greaterthan 2.8×10⁻³ lbs. per denier, greater than 3.0×10⁻³ lbs. per denier,greater than 4.0×10-3 lbs. per denier, greater than 5.0×10−3 lbs. perdenier, or greater than 6.0×10⁻³ lbs. per denier. The inventive flosshas increased surface roughness with an average roughness greater thanabout 0.3 microns (preferably about 1.3 microns), a root mean squareroughness of greater than about 0.35 microns (preferably about 1.6microns), and a peak to valley distance of greater than about 1.7microns (preferably about 6.3 microns). The dental floss may be anymaterial suitable for a floss, and porous PTFE is preferred,particularly expanded PTFE. There may be a plurality of fibers in thefloss, each with the same or different composition. The floss mayinclude a filler.

[0008] In another aspect, the present invention provides a method ofmaking a dental floss including the steps of providing a PTFE resin,extruding said resin to form an extrudate, and expanding the extrudateinto a fiber having the properties presented above. The extrusion isperformed in the preferred embodiment with a mandrel in the extruder.Reduction ratios in the extruder in various embodiments may be greaterthan 150 to 1, greater than 200 to 1, greater than 250 to 1, greaterthan 300 to 1, or greater than 500 to 1. The extrudate is heated duringexpansion by non-contact heating such that the extrudate does not touchthe heat source during the process.

[0009] In still another aspect, the present invention provides afilament having the properties and composition presented above.

[0010] In still further aspects, the present invention provides animproved sewing thread, a fiber for weaving, and a filament forstructures in bearing and bushing applications.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a cross-section of a dental floss according to anexemplary embodiment of the present invention;

[0012]FIG. 2 is a cross-section of a dental floss according to anotherexemplary embodiment of the present invention;

[0013]FIG. 3 is a side cross-sectional view of an extruder used toproduce the fiber according to this invention;

[0014]FIG. 3A is a side cross-sectional view of a portion of theextruder illustrated in FIG. 3;

[0015]FIG. 3B is a detail of a portion of FIG. 3A;

[0016]FIG. 3C is a detail of the tip extension used in Example 2;

[0017]FIG. 4 is a side view of equipment used in an exemplary embodimentof the process according to the present invention;

[0018]FIG. 5 is a side view of equipment used in another exemplaryembodiment of the process according to the present invention;

[0019]FIG. 6 is a perspective view of test apparatus used to measure theabrasion resistance of dental floss;

[0020]FIG. 7 is a side view of the test apparatus of FIG. 6;

[0021]FIG. 8 is a scanning electron micrograph at 100× magnification ofthe surface of a sample of dental floss according to an exemplaryembodiment of this invention;

[0022]FIG. 9 is a scanning electron micrograph at 100× magnification ofthe surface of a sample of conventional, prior art dental floss;

[0023]FIG. 10 is a scanning electron micrograph at 500× magnification ofthe surface of a sample of dental floss according to an exemplaryembodiment of this invention; and

[0024]FIG. 11 is a scanning electron micrograph at 500× magnification ofthe surface of a sample of conventional, prior art dental floss.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention provides an ePTFE dental floss having adensity less than 0.8 g/cc. The inventive floss is abrasion resistant,grippable, and has a good feel for the user.

[0026] PTFE dental floss is typically made by extruding and expanding arelatively large tape of PTFE, and then slitting the tape into fibers ofthe desired size for the dental floss. Such a production method isdescribed, for example, in U.S. Pat. No. 5,518,012 to Dolan et al.According to the present invention, the inventive dental floss isproduced by a novel method.

[0027] Specifically, according to the present invention, PTFE dentalfloss is produced by extruding a PTFE fiber (as opposed to a tape) ofdesired dimensions and then expanding the fiber to produce a node andfibril structure within the fiber that is characteristic of expandedPTFE. The expanded fiber has the desired final dimensions of the floss.In that manner, the floss fiber itself is produced from the extruderwithout the necessity of an intervening slitting step.

[0028] A PTFE fiber dental floss according to the present invention isproduced as follows. A PTFE resin is prepared for extrusion according tomethods known in the art, such as those described in U.S. Pat. No.3,953,566 to Gore, the disclosure of which is incorporated herein byreference. The extruder may be a conventional paste tubing extruder suchas that shown at 10 in FIG. 3. Extruder 10 includes a mandrel 11 in thecenter portion thereof. Mandrel 11 has a tip 12 (FIG. 3A) that extendsinto a die 13 at the opening of extruder 10. Extruder 10 has barrel 7and transition 8. The barrel has an inner diameter 1 as shown. FIG. 3Aillustrates the mandrel diameter 5. FIG. 3B illustrates the included dieland diameter dimension 2, and the tip land diameter dimension 4. FIG.3C illustrates the flattened tip land.

[0029] Mandrel 11 (and hence tip 12) may extend completely into die 13such that the extrudate from extruder 10 is hollow. Alternatively,mandrel 11 (and hence tip 12) may be withdrawn from die 13 back intoextruder 10 itself to reduce the relative size of the center hole orbore within the extrudate or to provide a non-hollow cross-section. Animportant aspect of the present invention is that the PTFE is exposed tosignificant working during extrusion. The amount of work imparted to thepolymer is affected by the reduction ratio of the extruder. Thereduction ratio is represented by the working area of the extruderdivided by the area of the die. To achieve the desired properties of thepresent invention, it is desirable that the reduction ratio be greaterthan 150:1, preferably greater than 200:1, more preferably greater than250:1, still more preferably greater than 300:1, and most preferablygreater than 500:1.

[0030] Whether a hollow fiber is produced or not according to thisinvention, and without being limited by theory, it is believed that useof mandrel 11 with tip 12 in the extrusion of a PTFE fiber providesadditional work to the PTFE that contributes to the beneficialproperties of the extrudate described herein.

[0031] Any desired operating conditions of extruder 10 may be used toproduce a suitable extrudate. Preferred conditions are set forth in theexamples herein.

[0032] After exiting extruder 10, the extrudate is spooled up on atake-up spool 40 (FIG. 4). The extrudate (shown at 41 in FIG. 4) is thenpaid off spool 40 and passed through an oven 42, preferably a forcedconvection oven. Capstans 43 and 44 are preferably used to control therate of extrudate 41 through oven 42. The extrudate is expanded as itpasses through oven 42. Any desired expansion (or stretch) ratio(determined by the capstan speed ratio) may be used; for example, from 2to 1 to 120 to 1 or greater. In an alternative embodiment, two separateovens 51 and 52 as shown in FIG. 5, and two separate correspondingexpansions, may be used. In either event, the process produces theinventive fiber 49, which may then be taken up on final take-up spool50.

[0033] An important feature of the invention is that all of the heatingof extrudate 41 (or fiber 49) occurs without contacting extrudate 41.Specifically, the present invention uses forced convection oven 42 (or51 and 52) through which extrudate 41 passes without contacting thewalls of the oven. This is in contrast to the currently accepted methodof producing PTFE dental floss that involves dragging a fiber over aheated plate in order to effect the heat transfer. Without being limitedby theory, it is believed that such contact with a heated plate smearsor otherwise smoothes the surface of the PTFE fiber, therebycontributing to the low surface friction and difficult grippability ofconventional PTFE flosses. As discussed in greater detail below, thenon-contact heating of the fiber of the present invention is believed tohelp produce a rougher surface on the fiber than is achieved with platecontact heating. This rougher surface in turn contributes to highersurface friction and better grippability for the inventive floss.

[0034] After expansion, the fiber has the desired final characteristicsof a dental floss. These final characteristics are, for example, athickness (designated “B” in FIG. 1) of 0.0015″ to 0.04″, a width(designated “A” in FIG. 1) of 0.3 to 4 mm (0.01″ to 0.16″), and a denierof 100 to 3,500. Most importantly, the fiber should have a density ofless than 0.8 g/cc, and in alternative embodiments less than about 0.7g/cc, less than about 0.6 g/cc, less than about 0.5 g/cc, less thanabout 0.4 g/cc, less than about 0.3 g/cc, and less than about 0.2 g/cc.Each of these properties is measured in a conventional manner. Thicknessmay be determined through any conventional means, such as through theuse of calipers, a snap gage, optical comparitors, or even a scanningelectron microscope. Density may be determined by dividing the measuredmass of a sample of fiber (without any coating or additive) by thecomputed volume of the sample. Volume may be computed by multiplying themeasured length, width, and thickness of the sample for substantiallyrectangular cross-sections, or by other known calculations for othercross-sectional shapes to obtain the most accurate approximation of thevolume. Denier is the measured mass of the sample (without any coatingor additive) in grams per 9000 meters of length.

[0035] The floss produced according to this method also has improvedabrasion resistance. Abrasion resistance is measured using the device 60illustrated in FIGS. 6 and 7. Device 60 has a base 61 made of stainlesssteel. Extension assemblies 62 and 63 project from base 61 and areadjustably attached thereto by bolts 69. Each extension assembly 62 and63 has a roller 64, 65 attached thereto by bolts 69. A micro graincarbide blade 66, part number AL-8 available from Micro-100, Inc. LosAngles, Calif., is supported on support 67 mounted in a groove 68 formedin base 61.

[0036] As shown in FIG. 7, a sample of floss 70 is laid over device 60such that floss 70 contacts device 60 at three points: at roller 64,blade 66, and roller 65. The angle of extension assemblies 62 and 63 isset so that floss 70 is as close as possible to base 61 without actuallytouching base 61. One end of floss 70 is attached to a 429 gram mass 100and the other end of floss 70 is attached to a reciprocating linearactuator (not shown) that repeatedly pulls floss 70 over device 60. Thereciprocating linear actuator has a stroke length of {fraction (13/16)}″and a rate of 1.5 strokes per second (each stroke is one back-and-forthcycle). Ten strokes are made. The reciprocating linear actuator is thenstopped, and floss 70 is removed from blade 66, which is wiped with aclean cotton towel. Floss 70 is then remounted and ten more strokes arerun. The reciprocating linear actuator is then stopped, and floss 70 isagain removed, blade 66 is again wiped with a clean cotton towel, andfloss 70 is then remounted and ten final strokes are run. Thus, a totalof 30 strokes are made with 2 intermittent cleaning wipes.

[0037] Floss 70 is removed from device 60 and extended between fiberjaws (horn type) of an Instron Model 1130, available from Instron Co.,Canton, Mass. Floss 70 is mounted with its abraded portion centeredbetween the jaws. The gauge length of the Instron is 10″ and thecross-head speed is 10″ per minute. The load at break (in pounds-force)is measured and recorded for each sample tested as “abrasion breakstrength.” Five such tests (abrading and breaking) are run on lengths ofeach fiber sample, and the average of the five is reported. The abrasionbreak strength may be divided by the denier of the tested sample toproduce a denier-normalized break strength. The term “abrasionresistant” as used herein means having a denier-normalized breakstrength according to the above test of greater than about 2.8×10⁻³lbs./denier. Data for the tested samples is reported in Table 7.

[0038] The inventive floss is considerably more grippable thanconventional PTFE fibers. Accordingly, the floss of the presentinvention may serve some flossing functions, such as use in a flosspick, without the need for any grip-enhancing coating or additive. Itmay be desirable, however, to include a light wax coating (such as 2-3%by weight of beeswax or any other known grip-enhancing coating oradditive) on the floss of the current invention to further enhancegrippability. Because of the increased grippability of the fiber itself,however, considerably less wax or other additive or coating need beapplied to the floss of the current invention compared to the amountnecessary with conventional PTFE flosses.

[0039] Without being limited by theory, it is believed that the improvedgrippability of the inventive floss is a result of its increased surfaceroughness and lower density over conventional PTFE flosses. Thisincreased surface roughness of the present fiber, which is at leastpartially a result of the non-contact heating of the fiber according tothe inventive method, is illustrated in the scanning electronmicrographs discussed below.

[0040] The surface roughness of the fibers is measured by profilometry.Measurements are taken from 500 micron by 500 micron squarerepresentative areas on the width side (designated “A” in FIGS. 1 and 2)of the sample.

[0041] Profilometery measurements were made with a Tencor Profiler ModelP_(—)10, which provides samples over a 500×500 micron area. The TencorProfiler was equipped with a MicroHead sr Exchangeable Measurement Head(stylus tip radius of 20 microns with an angle of 60 degrees). Menurecipe settings for the prolfilometer were as follows: Scan length:  500microns Data spacing in x: 0.40 microns Data spacing in y: 0.20 micronsNoise filter cutoff: .250 microns Waviness cutoff filter  250 microns

[0042] Surface roughness measurements are reported below.

[0043] The tensile strength (also referred to herein as “break strength”or simply as “strength”) of the inventive floss should be suitable foruse as a floss. Desirable strength is greater than 1.5 lbs. Preferably,the strength is greater than 2.0 lbs, greater than 2.5 lbs, greater than3.0 lbs, greater than 5.0 lbs, greater than 7.5 lbs, or greater than 10lbs. The strength of the floss is measured by a tensile tester, such asthe INSTRON machine mentioned above. The cross-head speed of the tensiletester is 10″ per minute. The gauge length was 10″ measured from tangentpoint to tangent point on horn-type jaws. The strength is considered tobe maximum load on the fiber during the test.

[0044] Matrix tensile strength of porous PTFE samples is determined bythe formula:

(2.2 g/cc×tensile strength)/density,

[0045] where 2.2 g/cc is taken to be the density of non-porous PTFE.

[0046] Tenacity is computed by converting the break strength fromlb-force to gram-force and dividing the filament's break strength ingram-force by the filament's denier.

[0047] The elongation of the fibers is calculated by the Instronmachine. Strain is calculated by dividing the length of the sample inthe Instron machine at failure by the original length of the sample.

[0048] A cross-section of an exemplary fiber made according to thisinvention is shown in FIG. 1. Fiber 20 has a substantially rectangularcross-section in FIG. 1. Upon extrusion from the extruder 10, theextrudate may have a round cross-section, but after the extrudate isstretched into a fiber and wound onto a spool, it is compressed somewhatto the substantially rectangular shape shown in FIG. 1. It will beappreciated by those skilled in the extrusion art that extrudate andfiber of any cross-sectional shape may be produced.

[0049]FIG. 2 shows another exemplary fiber 30 formed according to theprocess described above wherein the mandrel is inserted into the die farenough to produce a hollow cross-section. Although the hollow core ofthe fiber may ultimately be compressed after the fiber is expanded andwound onto the spool, the fiber initially has an opening 31 in thecenter of fiber 30 upon exiting extruder 10. In FIGS. 1 and 2, the widthdimension is generally designated as A and the thickness dimension isgenerally designated as B. The cross-sectional area is calculated as A×Bfor such substantially rectangular cross-sections. These dimensions areused in calculating the density as described above.

[0050] Although PTFE, and in particular expanded PTFE, is the preferredmaterial for use as the floss according to this invention, othermaterials including polymers such as polyethylene, ultra-high molecularweight polyethylene, polypropylene, and nylon may be used to producefloss having the inventive properties defined herein.

[0051] Any inventive fiber produced according to this invention mayoptionally include one or more fillers, also referred to as additives.The fiber has a structure of nodes interconnected by fibrils defininginterconnected passages and pathways. A filler may be included in thematrix of the ePTFE itself, or contained within the passages andpathways defined by the structure, or both. In the case of the inventivefiber with a hollow core (also referred to herein as a center bore orhole), a filler may also or alternatively be contained within the centerbore.

[0052] Desirable fillers or additives may include colorants, flavorants,medicants, anti-microbials, antibiotics, antibacterial agents,antifungals, dentifrice, remineralizing agents, whitening agents,immunological agents, anti-tartar or anti-caries agents, anti-plaqueagents, lysozmes, anti-inflammatory agents, hemostatic agents,analgesics, sodium fluoride, zinc chloride, tetrasodium pyrophosphate,sodium acid pyrophosphate, tetrapotassium pyrophosphate, vitamin K,water soluble calcium salts, blood factors that initiate the coagulationcascade, aminocaproic acid, tranexamic acid, adrenaline, alum,noradrenaline, iron salts and calcium alginate, sodiummonofluorophosphate, stannous fluoride, chlorhexidine, hexachlorophene,cetyl pyridinium chloride, benzethonium chloride, ureases, calciumcarbonate, magnesium carbonate, orthophosphoric acid, monosodiumphosphate, monopotassium phosphate, disodium phosphate, dipotassiumphosphate, hemisodium phosphate, benzothonium, chloride, acetyltrimethyl ammonium bromide, sanguinaria, triclosan, tetracycline, cetylpyridinium chloride, benzothonium chloride, melt emulsion ofdimethicone, and mixtures thereof. Any suitable gripping agent, such assilica, fumed silica, or sodium fluoride, or coating, such as wax, mayalso be used in order to make the inventive floss easier to grip,although as discussed herein, the inventive floss is more grippable thanconventional flosses without such agent or coating.

[0053] The following examples are presented by way of furtherexplanation and they are not intended, nor should they been interpreted,to limit the invention in any way.

EXAMPLE 1

[0054] (Hollow Floss Example)

[0055] Five pounds of CD123 PTFE resin available from ICI, Wilmington,Del., was sifted through a 10-mesh screen into a 2-gallon carboy andblended with 675 ml of Isopar K. (22.6% by weight of lube over dryweight of PTFE resin). The carboy was placed on an inclined plane tumbleblender and tumbled for 30 minutes. The carboy was then removed from theblender and allowed to sit overnight before pelletizing. The pre-formwas compressed to a pressure of 300 psi, removed from the pelletizer andplaced in a sealed tube to allow preheating. The pre-form was heated to40 degrees C. for a period of 16 hours before extrusion. The extruderused was a conventional paste tubing extruder using a 2-inch barrel. Thebarrel and die temperature were set to 40 degrees C. The die used forthe experiment had a land diameter of 0.153 inches. The tip used had aland diameter of 0.142 inches and was held in place by a 0.750 inchmandrel. The calculated reduction ratio for the set up was 1095 to 1. Awet extrudate was produced. The wet extrudate was taken up on a spoolwith a 4-inch core diameter using only enough tension to prevent slackfrom forming between the extruder and the spool. The extrusion rate wasabout 40 feet per minute. The wall thickness of the extrudate was about0.013 inch including die swell. The spool of wet extrudate was placed ona tension payoff and fed around a set of capstan wheels 5 inches indiameter. From the capstan, the extrudate was then passed through aforced convection oven 4 feet long with an inner diameter of 1 inchwithout contacting the walls of the oven. After leaving the oven, theextrudate was wrapped around a set of capstan wheels 7 inches indiameter. From the capstan wheels the extrudate was then passed througha second forced convection oven 4 feet long with an inner diameter of 1inch without contacting the walls of the oven. After leaving the oven,the extrudate was then wrapped around a set of capstan wheels 7 inchesin diameter and to a tension take-up using a 7.5-inch core diameterspool. The ovens were countercurrent flow ovens set to an airflow of 9cubic feet per minute. The temperature at the fiber exit of the ovenswas set at 380 degrees C. and the temperature at the fiber inlet of theovens was set at 220 degrees C. An initial speed ratio of 5 to 1 was setbetween the capstan 1 and capstan 2 with the first capstan rate set to 2feet per minute. The first capstan rate was maintained at 2 feet perminute for the entire test. The speed ratio between capstan 2 andcapstan 3 was set to 1.2 to 1 for this example. The ratio between thecapstan 1 and capstan 2 was then raised in steps of 5 until a speedratio of 15 to 1 was established. A length of material was run at thissetting before raising the speed ratio to 20 to 1. This process wasrepeated for speed ratios of 25 to 1 and 30 to 1. The oven temperatureswere raised along with the speed ratio, starting at the speed ratio of15 to 1, in 5-degree increments to maintain amorphous locking of thematerial. At the speed ratio between capstan 1 and capstan 3 of 36 to 1,the rate at the third capstans was 72 ft/min and the temperature of thefiber exit of the ovens was 400 degrees C. Markers were placed on theextrudate as it was taken up to identify where changes were made. As itwas taken up on a spool, the fiber tended to flatten out tosubstantially the shape shown in FIG. 1. The fiber obtained by thisprocess was tested for width, thickness, denier, and strength. Theresults are reported in Table 1 (Before the strength was measured, thesamples were coated with 2% natural beeswax. The beeswax was applied tothe samples using a winding and waxing machine model CE-1487 availablefrom Cezoma International, Inc., Spring City, Pa. The beeswax was heatedto 97 degrees Celcius before it was applied to the samples.)

EXAMPLE 2

[0056] (Hollow, Substantially Elliptical Cross-Section Example)

[0057] Using the same blended resin as in Example 1, an extrusion wasdone with the same die as in Example 1 and used a flattened tip having aprofile as shown at 200 in FIG. 3C. The reduction ratio for this setupwas about 265:1. The extrudate had a ‘D' shaped hole through its lengthto form the hollow fiber. The spool of wet extrudate was placed on atension payoff and processed in manner similar to Example 1. The speedratio between capstan 1 and capstan 2 was fixed at 4 to 1 and the speedratio between capstan 2 and capstan 3 varied as listed in Table 2. As itwas taken up on a spool, the fiber tended to flatten out tosubstantially the shape shown in FIG. 2. The spool of fiber producedaccording to this Example 2 were tested for width, thickness, denier,and strength, and the results are reported in Table 2. (Before thestrength was measured, the samples were coated with 2% natural beeswaxas described in connection with Example 1.) cl EXAMPLE 3

[0058] (Non-Hollow, Substantially Rectangular Cross-Section Example)

[0059] Using the same blended resin as in Example 1, an extrusion wasdone using a 0.075″ by 0.037″ rectangular die land cross section. Thetip tapered to a point and was withdrawn from contact approximately 0.5inches to allow a rectangular bead (non-hollow) to be extruded. Thebarrel size was 0.850 inches and the mandrel was 0.315 inch, giving acalculated reduction ratio of 176 to 1. The barrel and die temperaturewas set to 45 degrees C. for this example. The wet extrudate was takenup using the method of Example 1. The spool of wet extrudate was placedon a tension payoff and processed in manner similar to example 1. Thespeed ratios used for this Example 3 are noted in Table 3. The fiberobtained using this process was tested for width, thickness, denier, andstrength. The results are reported in Table 3. (Before the strength wasmeasured, the samples were coated with 2% natural beeswax as describedin connection with Example 1.)

EXAMPLE 4

[0060] (Non-Hollow, Substantially Round Cross-Section Example)

[0061] Using the same blended resin as in Example 1, an extrusion wasdone using a round cross section die with a 0.057″ land diameter andutilized the same tip used in Example 3 to allow a round bead(non-hollow) to be extruded. The barrel size was 0.650 inches and themandrel was 0.315 inch, giving a calculated reduction ratio of 99 to 1The barrel and die temperature was set to 45 degrees C. for thisexample. The wet extrudate was taken up using the method of Example 1.The spool of wet extrudate was placed on a tension payoff and processedin manner similar to example 1. Speed ratios used for this test arenoted in Table 4. The fiber obtained using this process was tested forwidth, thickness, denier, and strength. The results are reported inTable 4. (Before the strength was measured, the samples were coated with2% natural beeswax as described in connection with Example 1.)

EXAMPLE 5

[0062] (Non-Hollow Fiber Including an Additive)

[0063] CD 123 PTFE resin was blended with 10% by weight of SiO2. Thisresin was then blended with 320 ml/lb of isopropyl alcohol and allowedto sit overnight before pelletizing. A pre-form was compressed to apressure of 300 psi for the 0.850-inch barrel and preheated to 45degrees C. The pre-form was extruded using a 0.850-inch barrel, a0.315-inch mandrel, a 0.098-inch land diameter die and a 0.050-inch landdiameter tip. The calculated reduction ratio for this combination was 87to 1. The barrel and die temperature was set to 45 degrees C. for thisexample. The wet extrudate was taken up and processed using the methodof Example 1 with the following modifications: the first capstan ratewas set to 2 ft/min, a single forced-air oven was used with an ovenairflow of 10 cubic feet per minute, and an oven exit temperature of 375degrees C. Separate examples were prepared with speed ratios of 2 to 1,5 to 1, 10 to 1, 14 to 1, 18 to 1 and 27 to 1 to process the material.The samples produced using the process of this example was tested forwidth, thickness, denier, and strength. The results are reported inTable 5. (Before the strength was measured, the samples were coated with2% natural beeswax as described in connection with Example 1.)

[0064] A comparative sample of J&J Reach® Easy Slide® Mint floss wastested for certain properties for comparison with those measured for theinventive samples. The results of the comparative sample measurementsare reported in Table 6. As can be seen, the inventive fiber under allbut one set of conditions had a density considerably below that of thecomparative sample.

[0065] Certain samples from the above examples were separately testedfor abrasion resistance using the test described above. The inventivesamples were coated with 2% natural beeswax before abrasion testing. Thebeeswax was applied to the samples using a winding and waxing machinemodel CE-1487 available from Cezona International, Inc., Spring City,Pa. The beeswax was heated to 97 degrees Celcius before it was appliedto the samples. A comparative sample of J&J Reach® Easy Slide® Mintfloss was also tested for abrasion resistance. The results are reportedin Table 7.

[0066] The results show that the samples of the inventive fiber had ahigher abrasion resistance than the comparative sample as shown by thehigher denier-normalized break strength of the inventive fiber. Whenretested after the abrasion resistance testing, the inventive fiber alsoshowed much higher retained strength. This value is reported as strengthdecay in Table 7. (Note that because the original fiber sample wasbroken in the abrasion test to determine break strength, a siblingsample run through the abrasion test was used for this comparison. Anyapparent strength gain is considered within the experimental error andis reported as 0.) “Strength decay” is thus defined herein as thepercent strength loss by a fiber after undergoing the abrasion testdescribed herein. As shown in Table 7, the inventive fibers have anadvantageously lower strength decay compared to the comparative sample.The significantly improved strength decay of the inventive floss overthe comparative floss simulates performance in the mouth of a user. As auser moves the floss repeatedly between teeth, thereby subjecting thefloss to abrasion, it is important that the floss retain as muchstrength as possible to help prevent breakage. More strength will beretained by the inventive floss as indicated by its improved strengthdecay.

[0067]FIG. 8 shows the surface of the inventive floss of Example 1 (thesample with a total speed ratio of 24 to 1) at 100× magnification.Significant surface roughness is visible. FIG. 8 is to be compared withFIG. 9, which shows the surface at the same magnification of aconventional PTFE floss (J&J Reach® Easy Slide® Mint floss after itssurface coating has been stripped off by immersing the floss in xylenefor 10 minutes and then air-drying the floss). The striking differencein surface morphology between the inventive floss of FIG. 8 and thecomparative floss of FIG. 9 is surprising and unexpected. Thisunexpected result of such increased roughness of the surface morphologyfor the present invention is believed to produce the improvedgrippability, as well as other advantageous features, of the inventivefloss. FIGS. 10 and 11 further illustrate the point by making the samecomparison of surface morphology at 500× magnification. The surface ofthe inventive floss of Example 1 (the sample with a total speed ratio of24 to 1) shown in FIG. 10 is seen to be significantly rougher than thatof the comparative sample in FIG. 11 (J&J Reach® Easy Slide® Mint flossafter its surface coating has been stripped off as described above).

[0068] The surface roughness of the inventive floss of Example 1 (thesample with a total speed ratio of 24 to 1) and the comparative sample(J&J Reach® Easy Slide® Mint) were measured. Both samples were preparedby immersing the floss in xylene for 10 minutes and then air-drying thefloss. The results are reported below for the average roughness, theroot mean square roughness, and the peak to valley ratio measured by thedevice under the conditions set forth above. J&J Reach ® EasyMeasurement Inventive Fiber Slide ® Mint Average Roughness 1.306 micron.283 micron (Ra) Root Mean Square 1.570 micron .348 micron Roughness(Rq) Peak to Valley (Rt.) 6.316 micron 1.706 micron 

[0069] As can be seen from the data, the inventive fiber showsconsiderably greater roughness than the comparative sample as measuredby all of the reported features.

[0070] Again without being limited by theory, it is believed that thelow density and other features of the inventive PTFE floss compared toconventional PTFE flosses contributes significantly to the improvedproperties of the floss. These features of the invention help provide agrippable floss that has a rough feel in the mouth for enhancedperceived effectiveness, along with a desirable soft, compressible feelto the hands, while providing considerable material savings inproduction. The inventors have discovered that existing PTFE flosseshaving a density of greater than 0.8 g/cc cannot be made to have lowerdensity according to previously known production methods withoutsignificantly decreasing fiber strength. This invention provides a lowdensity PTFE fiber having the advantages mentioned herein as well ashaving strength suitable for use as a dental floss.

[0071] As an additional advantage, the inventors have discovered thatthe dental floss of the present invention has an even greater perceivedgrippability when the floss is wet. This should further enhance a user'sability to grasp the floss during use.

[0072] As referenced above, a particularly advantageous application ofthe present floss is for use with a floss device. Because of theimproved surface roughness and grippability of the inventive floss,devices may be molded having the inventive floss retained thereinwithout the need for grip-enhancing coatings or additives. The inventorshave produced samples of such floss devices, made of polypropylenesubstantially as described in European patent application publicationnumber EP 922440 A2, with the inventive ePTFE floss, and the floss wasadequately retained by the devices according to selected users inpreference tests.

[0073] In addition, the inventive process and fiber may be used in avariety of other applications. Although described herein in connectionwith a monofilament floss, a multifilament floss may be produced with aplurality of fibers according to this invention. The inventive fiber mayalso be combined, such as by twisting or joined with a binder, with aconventional floss fiber to form a composite floss.

[0074] In addition, an improved sewing thread is provided using thepresent invention's high porosity characteristic. Sewing threadstypically are coated or impregnated with a wax, oil or other lubricantto increase its processability during sewing operations. The increasedporosity over traditional ePTFE sewing threads provides for theincorporation and application of higher amounts of the lubricants.Additionally, the increased rough surface morphology of the presentinvention provides for protected regions where lubrications and or othercoatings may reside on the filament's surface. These regions may help tominimize the likelihood of the coatings being wiped off the filament'ssurface during sewing operations and other manufacturing and as wellduring the filament's use. An improvement to the duration of a lubricantor other coating or impregnation is believed to be increased as well dueto the fiber's higher loading and its increased surface roughness.

[0075] The present invention also provides for an improved bearing andor bushing material due to the increased filament's porosity and theability to impregnate the fibers with epoxies especially in the case ofbushing. The filament is woven into a sock configuration and epoxy isapplied around the woven sock. It is important that a bond between thewoven sock and the epoxy is achieved. The present invention provides asurface which has increased surface roughness which permits the epoxy toadhere to. Additionally, the present invention's increased porosityprovides for the epoxy or other flowable material to enter into theporous filament thus creating adhesion.

[0076] When filled with an electrical or a thermally conductivematerial, the invention provides for a filament with increasedelectrical and thermal resistance to density ratios. Moreover, since thepresent invention provides for filament with lower densities, the rangein which one can vary the filler content and density either bysubsequent compression or expansion or other means known in the art, thefilament's conduction and its resistance can be more broadly varied.

[0077] While particular embodiments of the present invention have beenillustrated and described herein, the present invention should not belimited to such illustrations and descriptions. It should be apparentthat changes and modifications may be incorporated and embodied as partof the present invention within the scope of the following claims. TABLE1 Thickness Width Weight denier density Break Tenacity MTS first ER 2ndER total ER (in) (mm) (g/ft) (g/9000 m) (g/cc) Strength (lb) (g/denier)(psi) 10 1.2 12 0.015 2.2 0.107 3159 0.42 10.2 1.47 40323 20 1.2 240.007 1.8 0.055 1624 0.56 7.8 2.18 59989 30 1.2 36 0.005 1.1 0.032 9450.75 5.7 2.74 75346

[0078] TABLE 2 Thickness Width Weight denier density Break Tenacity MTSfirst ER 2nd ER total ER (in) (mm) (g/ft) (g/9000 m) (g/cc) Strength(lb) (g/denier) (psi) 4 2.5 10 0.018 2.6 0.132 3898 0.36 13.5 1.57 432614 5 20 0.009 1.5 0.063 1860 0.60 8.8 2.15 59085 4 7.5 30 0.006 1 0.0441299 0.95 7.4 2.59 71141 4 10 40 0.005 0.8 0.029 856 0.94 5.7 3.02 831414 15 60 0.005 0.5 0.022 650 1.14 4.3 3.01 82677

[0079] TABLE 3 Thickness Width Weight denier density Break Tenacity MTSfirst ER 2nd ER total ER (in) (mm) (g/ft) (g/9000 m) (g/cc) Strength(lb) (g/denier) (psi) 10 1.2 12 0.017 1.5 0.079 2333 0.40 5.3 1.03 2837920 1.2 24 0.01 1.3 0,039 1152 0.39 3.85 1.52 41758 30 1.2 36 0.006 1.30.028 827 0.46 2.7 1.48 40789 40 1.2 48 0.007 1.5 0.033 974 0.41 3.11.44 39736 40 2 80 0.008 0.7 0.037 1093 0.85 3 1.25 34297 40 2.5 1000.003 0.3 0.01 295 1.44 1.3 2 54990

[0080] TABLE 4 Thickness Width Weight denier density Break Tenacity MTSfirst ER 2nd ER total ER (in) (mm) (g/ft) (g/9000 m) (g/cc) Strength(lb) (g/denier) (psi) 20 1.2 24 0.01 1.1 0.041 1211 0.48 2.5 094 2579330 1.2 36 0.007 1.1 0.023 679 0.39 2.2 1.47 40461 40 1.2 48 0.0045 10.019 561 0.55 1.6 1.29 35621 40 2 80 0.004 0.8 0.014 413 0.57 1.4 1.5442300

[0081] TABLE 5 thickness Width Weight/foot Density ER (inches) (mm)(g/ft) (g/cc) 0 0.035 3.9 0.828 0.78 2 0.033 3.5 0.378 0.42 5 0.023 3.30.185 0.32 10 0.008 3 0.042 0.23 14 0.013 2.9 0.07 0.24 18 0.013 3 0.0270.1 27 0.009 2.6 0.045 0.25

[0082] TABLE 6 Comparative J&J Sample Thickness Width Weight denierdensity Break Elongation Tenacity MTS (in) (mm) (g/ft) (g/9000 m) (g/cc)Strength (lb) at break (%) (g/denier) (psi) 0.0015 2.7 0.044 1300 1.46.61 12.3 2.31 63546

[0083] TABLE 7 Average Average Abrasion Break Abrasion Break StrengthStrength Sample Denier Density Strength Break strength per denier DecaySource (g/9000 m) (g/cc) (lbs) (lbs) (×1000) (%) Example 1 945 0.75 5.75.98 6.03 0 Example 2 1299 0.95 7.4 7.16 5.47 3.2, Example 3 1152 0.393.85 3.76 2.95 2.3 Example 3 827 0.46 2.7 2.72 3.39 0 J&J 1300 1.4 6.614.18 2.77 37

1. A dental floss comprising a polytetrafluoroethylene (PTFE) fiberhaving a denier between 100 and 3500 and a density of less than about0.7 g/cc.
 2. A dental floss as defined in claim 1, wherein said densityis less than about 0.6 g/cc.
 2. A dental floss as defined in claim 1wherein said density is less than about 0.5 g/cc.
 3. A dental floss asdefined in claim 1, wherein said density is less than about 0.4 g/cc. 4.A dental floss as defined in claim 1, wherein said density is less thanabout 0.3 g/cc.
 5. A dental floss as defined in claim 1, wherein saiddensity is less than about 0.2 g/cc.
 6. A dental floss as defined inclaim 1, wherein said density is about 0.6 g/cc.
 7. A dental floss asdefined in claim 1, wherein said fiber comprises expanded PTFE.
 8. Adental floss as defined in claim 1, wherein said fiber has a strengthsuitable for use as a dental floss.
 9. A dental floss as defined inclaim 1, wherein said fiber has a strength greater than about 1.5 lbs.10. A dental floss as defined in claim 1, wherein said fiber has astrength greater than about 2.0 lbs.
 11. A dental floss as defined inclaim 1, wherein said fiber has a strength greater than about 2.5 lbs.12. A dental floss as defined in claim 1, wherein said fiber has astrength greater than about 3.0 lbs.
 13. A dental floss as defined inclaim 1, wherein said fiber has a strength greater than about 5.0 lbs.14. A dental floss as defined in claim 1, wherein said fiber has astrength greater than about 7.5 lbs.
 15. A dental floss as defined inclaim 1, wherein said fiber has a strength greater than about 10 lbs.16. A dental floss as defined in claim 1, wherein said fiber is hollow.17. A dental floss as defined in claim 1, wherein said fiber has asubstantially elliptical cross-section.
 18. A dental floss as defined inclaim 1, wherein said fiber has a substantially circular cross-section.19. A dental floss as defined in claim 1, wherein said fiber has asubstantially rectangular cross-section.
 20. A dental floss as definedin claim 1, wherein said fiber is abrasion resistant.
 21. A dental flossas defined in claim 1, wherein said fiber has an average abrasion breakstrength greater than 2.8×10⁻³ lbs per denier.
 22. A dental floss asdefined in claim 1, wherein said fiber has an average abrasion breakstrength greater than 3.0×10⁻³ lbs per denier.
 23. A dental floss asdefined in claim 1, wherein said fiber has an average abrasion breakstrength greater than 4.0×10⁻³ lbs per denier.
 24. A dental floss asdefined in claim 1, wherein said fiber has an average abrasion breakstrength greater than 5.0×10⁻³ lbs per denier.
 25. A dental floss asdefined in claim 1, wherein said fiber has an average abrasion breakstrength of about 6.0×10⁻³ lbs per denier.
 26. A dental floss asdefined, in claim 1, wherein said fiber has a strength decay of lessthan 35%.
 27. A dental floss as defined in claim 1, wherein said fiberhas a strength decay of less than 10%.
 28. A dental floss as defined inclaim 1, wherein said fiber has a strength decay of less than 5%.
 29. Adental floss as defined in claim 1, wherein there are a plurality ofsaid fibers.
 30. A dental floss as defined in claim 1, wherein saidfibers contain a filler.
 31. A dental floss as defined in claim 31,wherein said fiber has a structure of an expanded PTFE matrix defininginterconnected passages and pathways, and said filler is disposed insaid passages and pathways.
 32. A dental floss as defined in claim 31wherein said fiber has a structure of an expanded PTFE matrix defininginterconnected passages and pathways, and said filler is disposed insaid expanded PTFE matrix.
 33. A dental floss as defined in claim 31,wherein said fiber has a center bore and said filler is disposed in saidcenter bore.
 34. A dental floss as defined in claim 31 wherein saidfiller comprises a grip enhancing material.
 35. A dental floss asdefined in claim 31 wherein said filler comprises a bioactiveingredient.
 36. A dental floss as defined in claim 31 wherein saidfiller is selected from the group consisting of colorant and aflavorant.
 37. A dental floss as defined in claim 1 further comprisingat least one coating over said fiber.
 38. A dental floss comprising atleast one fiber as defined in claim 1 and at least one other fiber,wherein said one fiber and said at least one other fiber are twistedtogether or joined together by a binder.
 39. A method of making a dentalfloss comprising the steps of (a) providing a PTFE resin, (b) extrudingsaid resin to form an extrudate, and (c) expanding said extrudate into afiber suitable for use as a dental floss.
 40. A method as defined inclaim 41, wherein said step of extruding said resin includes using areduction ratio of greater than 150:1.
 41. A method as defined in claim41, wherein said step of extruding said resin includes using a reductionratio of greater than 200:1.
 42. A method as defined in claim 41,wherein said step of extruding said resin includes using a reductionratio of greater than 250:1.
 43. A method as defined in claim 41,wherein said step of extruding said resin includes using a reductionratio of greater than 300:1.
 44. A method as defined in claim 41,wherein said step of extruding said resin includes using a reductionratio of greater than 500:1.
 45. A method as defined in claim 41 whereinsaid step of expanding said extrudate includes simultaneous non-contactheating of said extrudate.
 46. A dental floss as defined in claim 1 usedin a floss device.
 47. A floss device comprising a dental floss asdefined in claim 1
 48. A sewing thread comprising expanded PTFE having adenier between 100 and 3500, a density of less than about 0.7 g/cc and astrength of greater than about 1.5 lbs.
 49. A bearing comprisingexpanded PTFE having a denier between 100 and 3500, a density of lessthan about 0.7 g/cc and a strength of greater than about 1.5 lbs.
 50. Abushing comprising expanded PTFE having a denier between 100 and 3500, adensity of less than about 0.7 g/cc and a strength of greater than about1.5 lbs.
 51. A weaving fiber comprising expanded PTFE having a denierbetween 100 and 3500, a density of less than about 0.7 g/cc and astrength of greater than about 1.5 lbs.
 52. A dental floss comprising anexpanded PTFE fiber having surface characteristics of an averageroughness of greater than 0.3 microns, a root mean square roughness ofgreater than 0.35 microns, and a peak to valley distance of greater than1.7 microns.
 53. A dental floss as defined in claim 53 wherein saidaverage roughness is about 1.306 microns.
 54. A dental floss as definedin claim 53 wherein said peak to valley distance is about 1.570 microns55. A dental floss as defined in claim 53 wherein said peak to valleydistance is about 6.316 microns.
 56. A method of flossing teethcomprising the steps of (a) providing a dental floss comprising a fiberhaving a denier between 100 and 3500 and a density of less than about0.7 g/cc, and (b) inserting said dental floss between the teeth.
 57. Adental floss as defined in claim 1 wherein said dental floss has asurface with an average roughness of about 1.306 microns, a root meansquare roughness of about 1.570 microns, and a peak to valley distanceof about 6.316 microns.